Tissue reoxygenation following hypoxia is associated with ischemia-reperfusion injury (IRI) and may signal the development of ischemic preconditioning, an adaptive state that is protective against subsequent IRI. Here we used microarray RNA analysis of in vivo and in vitro models of IRI to delineate the underlying molecular mechanisms. Microarray analysis of renal tissue after ischemia-reperfusion revealed a number of highly up-regulated antioxidant genes including aldehyde dehydrogenases (ALDH1A1 and ALDH1A7), glutathione S-transferases (GSTM5, GSTA2 and GSTP1), and NAD(P)H quinone oxidoreductase (NQO1). The transcription factor NF-E2-related factor-2 (Nrf2), a master regulator of this antioxidant response, is also elevated in IRI. Furthermore, microarray analysis of renal epithelial cells exposed to hypoxia/reoxygenation identified Nrf2 to be up-regulated on reoxygenation. We also reveal a reoxygenation-specific nuclear accumulation of Nrf2 protein and subsequent activation of a NQO1 promoter reporter construct. Attenuating reactive oxygen species (ROS) in reoxygenation using the antioxidant N-acetyl cysteine results in inhibition of Nrf-2 activation. mRNA levels for Nrf2-dependent genes were detected in human liver biopsy 1 h after transplantation. These results indicate that reoxygenation-dependent Nrf-2 activity facilitates ischemic preconditioning through the induction of antioxidant gene expression and that ROS may be critical in signaling this event.

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Lipoxins are lipoxygenase-derived lipid mediators with both anti-inflammatory and proresolution properties that have been demonstrated in vivo and in vitro. The bioactivity profile of lipoxins in vitro suggests that they have therapeutic potential in acute renal failure and glomerulonephritis; predictions that have been borne out to date in experimental models of renal disease. We review recent developments on the molecular basis of lipoxin bioactions mediated through receptor crosstalk and the accumulating evidence that lipoxins may have potential as novel anti-inflammatory agents.

Treatment with the lipoxin analog 15-epi-16-(FPhO)-LXA4-Me prior to injury modified the expression of many differentially expressed pathogenic mediators, including cytokines, growth factors, adhesion molecules, and proteases, suggesting a renoprotective action at the core of the pathophysiology of acute renal failure (ARF). Importantly, this lipoxin-modulated transcriptomic response included many genes expressed by renal parenchymal cells and was not merely a reflection of a reduced renal mRNA load resulting from attenuated leukocyte recruitment. The data presented herein suggest a framework for understanding drivers of kidney injury in ischemia/reperfusion and the molecular basis for renoprotection by lipoxins in this setting.

The histologic associations and clinical implications of peritubular capillary C4d staining from long-term renal allografts are unknown. We identified 99 renal transplant patients who underwent an allograft biopsy for renal dysfunction at least 10 yr after transplantation, 25 of whom were C4d-positive and 74 of whom were C4d-negative. The average time of the index biopsy from transplantation was 14 yr in both groups. Compared with C4d-negative patients, C4d-positive patients were younger at transplantation (29 Ϯ 13 versus 38 Ϯ 12 yr; P Ͻ 0.05) and were more likely to have received an allograft from a living donor (65 versus 35%; P Ͻ 0.001). C4d-positive patients had more inflammation, were more likely to have transplant glomerulopathy, and had worse graft outcome. The combined presence of C4d positivity, transplant glomerulopathy, and serum creatinine of Ͼ2.3 mg/dl at biopsy were very strong predictors of rapid graft loss. C4d alone did not independently predict graft loss. Retrospective staining of historical samples from C4d-positive patients demonstrated C4d deposition in the majority of cases. In summary, these data show that in long-term renal allografts, peritubular capillary staining for C4d occurs in approximately 25% of biopsies, can persist for many years after transplantation, and strongly predicts graft loss when combined with transplant glomerulopathy.